We are using drugs that stop some normal cells in the GO part of the cell cycle but do not arrest transformed cells derived from them, to develop an in vitro test for loss of growth control. We are looking for other drugs that, in a similar way, distinguish between normal and neoplastic transformed cells. We wish to determine whether transformation is always accompanied by this loss of growth inhibition by drugs, or whether there are other modes of transformation. New human and hamster lines of spontaneously transformed, naturally occurring (tumor) and chemically transformed cells will be tested. The flow microfluorimeter and radioactive thymidine incorporation will be utilized to follow the cell-cycle events. Studies also will be pursued to determine the biochemical basis for the different action of these drugs on the normal and transformed cells.